UNIVERSITY   OF   CALIFORNIA 

COLLEGE    OF    AGRICULTURE 

AGRICULTURAL    EXPERIMENT   STATION 

BERKELEY,    CALIFORNIA 


THE  ELECTRIC  BROODER 


B.  D.  MOSES  AND  T.  A.  WOOD 


BULLETIN  441 

November,  1927 


UNIVERSITY  OF  CALIFORNIA  PRINTING  OFFICE 

BERKELEY,  CALIFORNIA 

1927 


FOREWORD 

This  bulletin  is  a  contribution  of  the  Division  of  Agricultural 
Engineering,  University  of  California,  and  the  Poultry  Sub-Com- 
mittee of  the  California  Committee  on  the  Relation  of  Electricity  to 
Agriculture.  It  is  the  second  of  a  series  planned  to  report  the  results 
of  investigations  conducted  jointly  by  the  Agricultural  Experiment 
Station,  College  of  Agriculture,  University  of  California,  and  the 
California  Committee  on  the  Relation  of  Electricity  to  Agriculture. 
This  committee  represents  the  agricultural  and  electrical  industries 
in  California  that  are  working  together  for  the  purpose  of  making 
available  reliable  information  concerning  the  use  of  electricity  on  the 
farm,  and  cooperating  with  similar  committees  in  other  states.* 

E.  D.  Merrill,  Director, 
California  Agricultural  Experiment  Station. 


*  The  personnel  of  this  committee  for  1926-27  is: 

E.  D.   Merrill,   Dean,   College   of   Agriculture,   University   of   California, 

Berkeley,  Chairman. 
N.  E.  Sutherland,  Pacific  Gas  &  Electric  Co.,  San  Francisco,  Treasurer. 

B.  D.  Moses,  College  of  Agriculture,  Davis,  State  Director  and  Secretary. 
T.  A.  Wood,  Davis,  Field  Engineer. 

F.  E.  Boyd,  General  Electric  Company,  San  Francisco. 

C.  L.  Cory,  Dean,  College  of  Mechanics,  University  of  California,  Berkeley. 
H.  M.  Crawford,  Pacific  Gas  &  Electric  Co.,  San  Francisco. 

J.  J.  Deuel,  California  Farm  Bureau  Federation,  San  Francisco. 

A.  M.  Frost,  San  Joaquin  Light  &  Power  Corporation,  Fresno. 
Alex.  Johnson,  California  Farm  Bureau  Federation,  Berkeley. 
T.  H.  Lambert,  El  Monte,  Agriculturist. 

B.  M.  Maddox,  Southern  California  Edison  Co.,  Visalia. 

W.  C.  McWhinney,  Southern  California  Edison  Co.,  Los  Angeles. 

C.  Grunsky,  California  Bailroad  Commission,  San  Francisco. 


THE  ELECTRIC  BROODER 

B.  D.  MOSES*  and  T.  A.  WOOD2 


INTRODUCTION 

' '  A  brooder  is  a  covered  and  warmed  receptacle  for  the  protection 
of  chicks  reared  without  a  hen."  The  heat  required  can  be  supplied 
by  the  combustion  of  fuel  or  by  electricity.  The  universal  demand 
for  labor  saving  devices  which  are  automatically  controlled  has 
resulted  in  the  adoption  by  many  farmers  of  brooders  heated  by 
electricity.  Statistics  indicate  that  at  least  five  thousand  of  these 
units  were  in  use  in  California  in  1926. 

In  order  to  make  this  type  of  energy  applicable  to  brooding,  heat 
conservation  is  necessary.  This  has  been  effected  in  some  cases  by  the 
use  of  heat  insulation  on  the  hover;  in  others  by  curtains  around  the 
outer  edge  of  the  hover ;  and  again  at  other  times  by  crowding  chicks 
together,  making  use  of  the  body  heat.  On  account  of  poor  ventilation 
and  this  crowding,  losses  have  resulted  which  have  sometimes  been 
attributed  to  the  use  of  electrically  generated  heat  rather  than  to 
defects  in  brooder  design  and  to  improper  manipulation. 

The  purpose  of  this  bulletin  is  to  report  results  of  observations  on 
brooders  heated  by  electricity  in  actual  field  operation  from  the  stand- 
point of  general  design,  mechanical  features,  power  requirements,  and 
heating  costs. 

ELECTRIC    BROODER    REQUIREMENTS 

In  the  profitable  brooding  of  chicks  certain  essential  requirements 
have  to  be  met.    Some  of  the  more  important  are : 

1.  At  least  seven  square  inches  of  free  floor  space  beneath  the 
brooder  should  be  provided  for  each  chick. 

2.  Sufficient  heat  must  be  available  to  maintain  a  temperature  of 
90  to  95  degrees  Fahrenheit  two  inches  above  the  floor  and  five  inches 
inside  the  outer  edge  of  the  hover  under  all  weather  conditions. 


1  Assistant  Professor  of  Agricultural  Engineering  and  Associate  Agricultural 
Engineer  in  the  Experiment  Station. 

2  Field    Engineer,    California    Committee    on    the    Relation    of    Electricity    to 
Agriculture. 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

3.  The  heating  elements  should  be  so  arranged  as  to  obtain  a 
uniform  distribution  of  heat  and,  if  possible,  to  assist  in  ventilation. 

4.  A  thermostat  for  temperature  regulation  should  be  provided. 

5.  Adequate  ventilation  is  essential  to  introduce  fresh  air  and  to 
remove  the  excess  carbon  dioxide,  water  vapor,  and  other  impurities 
as  they  are  formed. 

6.  The  brooder  should  be  simple  and  well  built.  It  should  be  so 
designed  and  constructed  as  to  simplify  operation,  minimize  costs  and 
insure  satisfactory  brooding  conditions. 

7.  The  first  cost  as  well  as  operating  costs  must  be  such  as  to  render 
the  use  of  the  brooder  profitable. 


HEAT   AND    VENTILATION    PRINCIPLES    INVOLVED 

The  temperature  of  a  body  is  due  to  the  presence  of  heat  in  that 
body,  and  while  there  is  but  one  kind  of  heat  of  which  we  have  any 
knowledge,  there  are  three  known  methods  (convection,  conduction, 
and  radiation)  by  which  this  heat  can  be  transferred  from  one  body 
to  another. 

Convection  is  the  transfer  of  heat  from  the  source  to  the  absorber 
by  storing  the  heat  temporarily  in  a  carrier  substance,  such  as  air  or 
water,  and  then  bodily  moving  this  substance  from  the  source  to  the 
cooler  heat  absorber.  For  example,  a  living  room  is  heated  by  a 
furnace  in  the  basement.  The  heat  is  generated  in  the  basement,  is 
stored  temporarily  in  the  air  above  the  furnace,  and  is  allowed  or 
caused  to  move  by  convection  (air  currents)  to  the  living  room. 

Conduction  is  the  transfer  of  heat  from  one  small  particle  of  a 
substance  to  the  next,  by  contact  of  these  particles  or  their  near  asso- 
ciation, along  the  length  or  breadth  of  the  substance.  The  fire  in  a 
stove,  for  instance,  generates  heat,  which  warms  the  inner  surface  of 
the  stove  metal.  The  particles  on  the  inner  surface  of  the  metal  pass 
this  heat  along  to  the  next  until  the  heat  appears  on  the  outside  sur- 
face of  the  stove.  The  outside  surface  is  not  in  contact  with  the  heat 
source  but  is  heated  by  conduction  from  a  surface  which  is  in  direct 
contact.  In  gases  and  liquids,  this  action  is  comparatively  slow,  but 
in  most  metals  it  is  much  more  rapid.  The  amount  of  heat  transferred 
depends  upon  the  difference  in  temperature  between  the  inside  and 
outside  surfaces,  the  thickness  of  the  substance  through  which  it  must 
pass,  the  area  of  this  exposed  surface,  and  the  ability  of  the  substance 
to  transfer  heat. 


BuL.  441]  THE   ELECTRIC    BROODER  5 

Radiation  is  the  transfer  of  heat  through  space  by  means  of  vibra- 
tions in  the  ether.3  This  is  the  most  common  type  of  heat  transfer, 
since  practically  all  heat  upon  the  surface  of  this  planet  comes,  or  has 
come,  directly  or  indirectly  from  the  sun  by  radiation.  Heat  in  this 
form  is  transferred  with  the  speed  of  light,  namely,  186,000  miles  per 
second,  and  requires  no  material  substance  for  this  transfer.  These 
vibrations  or  waves,  do  not  become  sensible  heat,  until  they  are 
absorbed  by  some  substance  such  as  the  earth.  The  amount  of  heat 
transferred  from  the  source  to  the  absorber  depends  upon  the  size, 
nature,  and  surface  temperature  of  the  exposed  radiating  body,  upon 
the  distance  through  which  the  heat  must  be  radiated,  and  upon  the 
ability  of  the  cooler  body  to  absorb  the  heat  vibrations. 

Heat  reflectors:  Radiated  heat,  like  light,  can  be  reflected  without 
great  loss  if  proper  reflecting  surfaces  are  used.  The  amount  of  heat 
lost  depends  upon  the  surface  condition  of  the  reflector,  upon  the 
color  of  the  reflector  surface,  and  upon  the  substance  of  which  it  is 
made.  Black,  rough  surfaces,  for  instance,  will  absorb  practically  all 
heat  rays  striking  them,  while  a  light  polished  metal  surface  may 
reflect  80  per  cent  of  these  rays.  The  direction  of  travel  of  reflected 
heat  rays  can  be  controlled  by  the  use  of  concave,  flat  or  convex 
reflectors.  The  sharpness  or  abruptness  of  the  concentration  or  diffu- 
sion depends  upon  the  radius  of  curvature  of  the  reflector.  By  proper 
reflector  designs  then,  radiated  heat  can  be  concentrated  within  a 
small  area  or  can  be  diffused  to  almost  any  degree  desired. 

Ventilation:*  A  brooder  must  be  adequately  ventilated,  since  water 
vapor,  carbon  dioxide,  and  other  gases  given  off  by  the  chick  tend  to 
accumulate  beneath  the  hover  when,  for  example,  curtains  are  used 
or  ventilation  is  otherwise  more  or  less  restricted.  Water  vapor  has, 
in  some  instances,  accumulated  to  such  an  extent  as  to  result  in  high 
mortality  to  the  chicks. 

3  These  vibrations  or  waves  exist  in  nature  in  various  forms.  Sound,  as  an 
illustration,  is  transferred  through  matter  by  vibrations  or  waves  in  the  sub- 
stance surrounding  or  adjoining  the  sound  source.  Heat,  light,  and  electricity 
require  no  such  material  substance  for  their  transfer  when  in  wave  form,  but 
are  propagated  instead  with  great  speed  through  what  appears  to  be  empty 
space,  but  which  is  supposed  by  physicists  to  be  filled  with  an  immaterial, 
perfectly  elastic,  and  weightless  substance  called  ether. 

*  "Ventilation  consists  in  displacing  vitiated  air  from  an  apartment  and 
replacing  it  with  fresh  air."  All  the  foul  air  is  not  displaced  bodily  at  one 
time,  but  is  diluted  by  the  incoming  fresh  air  until  it  is  suitable  for  respira- 
tional  purposes.  There  are  two  methods  of  obtaining  this  ventilation,  namely, 
by  "natural"  ventilation,  in  which  the  air  movements  are  induced  by  a 
"thermal"  head;  and  by  "mechanical"  ventilation,  in  which  the  air  move- 
ments are  maintained  by  a  power-driven  fan.  All  brooders  tested  used  the 
natural  system.  However,  in  some  cases  the  air  flow  was  intensified  by 
artificial  heat  which  was  installed  at  advantageous  points  in  the  system. 


b  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

The  ability  of  the  brooder  air  to  absorb  this  water  vapor  is  limited 
by  its  temperature,  volume,  pressure,  and  humidity.  Air  which  has 
absorbed  all  the  water  vapor  possible  is  said  to  be  "saturated"  or  to 
have  a  "relative  humidity"  of  100  per  cent.  If  saturated  air  comes 
in  contact  with  a  surface  cooler  than  this  air,  its  temperature  drops 
and  its  volume  and  water  absorbing  capacity  decrease.5  This  causes 
"condensation"  and  dew  is  formed  upon  the  cooler  surface. 

Ventilation  for  the  purpose  of  removing  impure  air  and  introduc- 
ing fresh  air  affects  both  the  amount  of  heat  used  and  the  quality  of 
chick  produced ;  but  the  health  of  the  chick  should  never  he  jeopardized 
in  order  to  save  a  little  heat.  The  slight  cost  of  the  additional  heat 
necessary  to  secure  adequate  ventilation  is  more  than  offset  by  the 
lower  mortality  of  chicks  and  by  the  stronger  chicks  which  are 
produced  when  all  conditions  are  fully  met. 


ECONOMICS  OF  NEW  DEVICES 

Many  devices  are  being  developed  to  reduce  brooding  costs  either 
by  saving  heat  or  by  increasing  the  number  of  chicks  that  can  be 
taken  care  of  under  the  hover.  These  devices  may  be  in  the  form  of 
adequate  heat  insulation,  a  thermostat  switch,  or  a  different  type  of 
heating  or  ventilating  system ;  and  they  may  effect  a  saving  by  reduc- 
ing the  mortality,  or  by  decreasing  the  amount  of  heat  and  of  labor 
required.  Before  any  new  brooding  device  is  purchased,  the  pros- 
pective customer  should  determine  whether  there  really  will  be  a 
saving  effected  by  its  use,  since  the  additional  money  that  can  be 
economically  invested  in  any  device  is  limited  by  the  returns  which 
that  device  will  earn. 


NON-GLOWING     (BLACK    HEATe)     TYPES    OF    BROODERS    STUDIED 

The  oldest  type  of  electric  brooder  which  seems  to  be  economically 
successful,  in  so  far  as  heating  costs  are  concerned,  consists  of  a 
rather  low  hover  surrounded  by  curtains  and  heated  by  overhead  non- 


5  The  ability  of  air  to  absorb  water  vapor  is  doubled  for  each  27  to  30°  F 
rise  in  temperature  and  conversely  is  halved  for  each  27  to  30°  F  drop  in  tem- 
perature (within  all  practical  limits  of  temperatures  encountered).  Air  cannot 
sustain  a  humidity  greater  than  100  per  cent.  Should  a  drop  in  temperature 
occur  to  such  air,  enough  vapor  condenses  out  to  establish  equilibrium  again. 

6 ''Black  heat'*  is  a  term  sometimes  applied  to  the  heat  from  electric 
heating  elements,  which  operate  at  a  temperature  below  the  glow  point;  that 
is,  the  wire  maintains  its  natural  color  (see  fig.  21).  "Convection"  brooders 
are  those  in  which  this  method  of  heat  transfer  predominates. 


Bul.  441] 


THE   ELECTRIC    BROODER 


glowing  heating  elements  (see  figs.  1,  2,  and  sketch  No.  1,  fig.  3). 
These  heating  elements  are  fastened  to  the  under  side  of  the  hover 
just  above  the  heads  of  the  chicks.  The  temperature  of  the  air  in  the 
brooder  is  controlled,  in  so  far  as  the  electric  heat  used  is  concerned, 
by  a  thermostat  switch.  No  definite  provision  has  been  made  in  this 
type  of  brooder  to  induce  positive  ventilation.  When  used  with  a 
relatively  small  number  of  chicks  scattered  over  a  large  brooder  floor 
area,  this  early  form  is  fairly  satisfactory. 


Pig.  1. — A  simple  box  type,  non-glowing  or  convection  electric  brooder, 
using  " overhead"  heat.  Note  the  use  of  good  electric  insulation,  an  ether 
wafer  thermostat  switch,  and  well  designed  power  leads  as  well  as  the 
simplicity  of  the  hover  construction. 


Sketch  No.  2  (fig.  3)  shows  the  usual  hover  employing  overhead, 
non-glowing  elements  and  fitted  with  a  chimney  and  damper  in  the 
apex  of  the  cone.  Since  warm  air  tends  to  rise,  this  method  of  con- 
necting the  confined  brooder  air  with  the  room  air,  permits  the  heat 
generated  by  the  heating  elements  to  escape  through  the  stack,  even 
though  the  damper  is  but  slightly  open. 

Sketch  No.  3  (fig.  3)  is  a  further  modification  of  the  chimney  idea, 
using  a  stack  which  extends  down  into  the  brooder,  and  which  may  be 
of  one  piece  or  of  the  telescoping  type.  The  telescoping  stack  can  be 
adjusted  until  a  place  is  reached  where  the  temperature  difference  is 


8  UNIVERSITY    OP    CALIFORNIA EXPERIMENT    STATION 

just  enough  to  induce  the  proper  ventilation  of  the  brooder.  This 
device  prevents  the  waste  of  heat  that  may  occur  in  the  type  just 
mentioned.  It  depends  for  its  success  upon  manual  control.  Failure 
to  adjust  the  stack  for  changing  temperature  and  moisture  conditions, 
however,  is  a  source  of  trouble.  The  air  flows  in  under  the  curtain  at 
the  edge  and  out  through  the  stack,  an  arrangement  which  leaves  the 
chicks  which  are  near  the  curtain,  in  a  cool  draft. 


U  i-AJJJMm 


Fig.  2. — A  conical  galvanized  iron  non-glowing  or  convection  type  electric 
brooder,  using  overhead  heat. 

a.  Side  view  showing  the  low,  well  constructed  conical  hover.  This  brooder 
can  be  placed  under  the  dropping  board  or  in  other  small  compartments  and 
allowed  to  rest  on  its  own  legs  or  it  may  be  suspended  from  the  ceiling  by  a 
hook  at  the  apex  of  the  cone. 

b.  A  view  from  beneath,  showing  a  good  type  of  electric  wiring.  The 
heating  elements  are  wound  on  asbestos  sticks  and  are  fastened  to  the  hover 
by  spring  clips.  Should  the  wire  on  one  stick  burn  out  it  is  easily  removed  and 
a  new  one  snapped  into  place.  Note  that  two  heating  circuits  are  connected 
in  parallel,  thus  assuring  some  heat  should  one  circuit  burn  out. 


Bul.  441J 


THE   ELECTRIC    BROODER 


LINE   SHETCM   NO.    1. 
HEAT:    Blacn,  Overhead  Heating  Elements. 

CONTROL  :    Thermostat  Switch. 
VENTILATION:  Room  Cross  Currents, Undirected. 

CURTAINS:   Two. 

AIR  FLOW.  Jn  at  One.  Side,  Out Other  Side 
BROODER  FLOOR:  Room 


rfT   f         I         \>ft 


LINE.    SKETCH    Alt  2 
HEAT:  B  la  CM,  Over head  Heot inq  Elements. 

CONTROL:  Thermostat  Switch. 
VENTILATION:  Forced,  Directed. 

CURTAINS:  One.       CHIMNEY:  At  Apex. 

AIR  FLOW:  In  of  Curtain,   Out  Thru  Stocrt. 
BROODER  FLOOR:  Room. 


MJ. 
HEAT:  B/ach,  Overhead  Heating  Elements. 

CONTROL:    Thermostat  Switch. 
VENTILATION:  Semi-d, reeled ',  Slightly  Forced, 

According  to  Height  ofStocJffrom  Floor. 

CURTA  INS :  One .  CMIMNE  V.  Telescoping. 

AIR  FLOW:  In  at  Curtain, Out  StacK;  or  In  at 

One  Side  Out  Other  Side;  or  Both. 
BROODER  FLOOR:  Room. 


HEAT:  Blacn,  Overhead  Heating  Elements. 

CONTROL:   Thermostat  Switch. 
VENTILATION:  Sem.-directed,  Slightly  Forced, 

According  to  Height  of  Hover  from  Floor. 

CURTAINS:  One.         FLOOR  AIR  DUCT:  One. 

AIR   FLOW:  In  at  Center  Air  Duct,  Out  Under 

Curtain;  In  at  One  Side, Out  Other j  or  Both. 
BROODER  FLOOR:  Room. 


hAs. 
HEAT:  BIocm,  Overhead  hefting  Elements 

CONTROL  :  Thermostat  Switch. 
VENTILATION:  Room  Cross  Currents,  Undirected. 

CURTAINS:  One,  or  Two. 

AIR  FLOW:  In  at  One  Side,  Out  Other  Side. 
BROODER  FLOOR:  False  Slatted  Floor,  Covered 

With  Burlap,  Standing  2  "above  Ffoom  Floor. 


HEA  T:  Blacn  Overhead  Heating  Elements. 

CONTROL:  Thermostat  Switch. 
VENTILATION:  Forced,  Directed. 

CURTAINS:  One.     AIR  DUCT:  One,  Center. 

AIR  DUCT  ELEMENT.    Slowing  Coil. 

AIR  FLOW:  Jn  at  Center  Air  Duct,  Out  Under 

Curtain. 
BROODER  FLOOR :  Room. 


HEAT:  Blacx, Overhead  heating  Elements. 

CONTROL:  Thermostat  Switch 
VENTILATION:  Room  Cross  Currents,  Undirected. 

CURTAINS:  One 

FALSE  FLOOR  ELEMENT:  Blacx   heat. 

AIR  FLOW:  In  at  One  Side,  Out  Oth  tr 
BROODER  FLOOR:  Special  Heated  Floor 
Standing  4"  Above  Hoom  Floor,  A/o  Air  Duct. 


m  8. 

HEAT:  Blacn  Overhead  Heating  Elements. 

CONTROL:  Thermostat  Switch. 
VENTILATION:  Forced,  Directed. 

CURTAINS:  One.    AIR  DUCT:   One, or  Two. 

FALSE  FLOOR  ELEMENTS:  Blacn  heat. 

AIR  FLOW:  Under  False  Floor,  Up  Thru  Duct, 

Out  Under  Curtain. 
BROODER  FLOOR:  Special  Heoted  Floor. 

4-'  Above  Room  Floor. 


Fig.  3. — Line  sketches  of  brooders  studied. 


10 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


N&9. 
HEAT:  Glowing  or  BlacK  F/oorFfeoflng  Elements. 

CONTROL  :  Thermostat  Snitch. 
VENTI LATION:  Semi -directed,  Slightly  Forced. 

According  to  Height  of  Curiam  from  Floor. 

CURTAINS:  One.  AIR  DUCT:    One. 

AIR  FLOW :  In  Thru  Tunnel,  Out  Under  Curtain 
BROODER  FLOOR:  Room. 


AtPll. 

HEAT:  C  lowing,  Overhead  Healing  Elements. 
REFLECTOR:  Tin,  Concave,  20"  Radius, 
CONTROL :  danual.  CURTAINS:  None. 

VEIV  TILA  TlON:  Cross  CWrcn  h.  Undirected. 


-I 


J 


Hi  10 
HEAT:  Globing  or  Glac/r  Side  Floor' Elements. 

CONTROL:  Thermostat  Snitch. 
VENTILATION:  Forced,  Directed. 

CURTAINS:  One. 

AIR   FLOW:  In  thru  Side  Vent,  Over  Partition, 

Across  Brooder,  Out  Under  Curtain. 
BROODER  FLOOR:  Room. 


m\I2. 
HEAT:  G/owing,  Overhead  Heating  Elements 

REFLECTOR:  Tin,  Rt,  Vert-,Cene. 

CONTROL  :  Manual  'r-  7hermostaf  Switch. 
VENTILATION:  Cross  Currents,  Undirected. 

CURTAINS:  None.  AIR  DUCTS:  Hone. 

AIR  FLOW:   As  Flowing  in  Room 


Hi  13. 

HOVER:  Same  as  Used  in  /V*  12. 

REFLECTOR:  Inverted  D<shpan  Type,  Which 
Is  anlmprovement  over   those  used  in  A/&, 
J  J  and  12,  Since  it  Diffuses  the  Raf  some  - 
nhai,  Thus  fending  toTron  Out  fne  'Hoi  Spot " 
At  the  Center  of  the  Ho  ver. 


N&14. 

HOVER  :  Same  as  Used  in  Rsj2. 

REFLECTOR:  Convey,  20"  Radius,   k/ith 
Heating  Elements  JO"  Centers,  Preferably 
Three  in  number.    By  using  Correct  ffadius 
cfCu'rvot^/'e   almost  any  degree  of  ray  dif- 
fusion can  be  obtained. 


N&JS. 
REFLECTOR:  Right  Inverted  Cone.    This 
Typ«  should  not  be  used  Unless  the  ratio 
of  height  to  dioneter  is  1  to  4~  or  more, 
since  it  vitf  produce  a  'not spot." 
similar  to   NBS-  II  and  12. 


Ate  16. 
REFLECTOR:    Convex  Center  Portion,  20" 
to  24"  Radius';  Concave  Rim,  J' to  4" Radius. 
This  Reflector,  property  designed,  rVi/l 
give  even  heat  distribution  and  Form 
no  he  of  'poc/tet '  nrhcre  it  meets  the 
hover  sides. 


Fig.  4. — Continuation  of  series  shown  in  figure  3. 


Bul.  441] 


THE   ELECTRIC    BROODER 


11 


Fig.  5. — A  conical,  galvanized  iron,  non-glowing  or  convection  type  electric 
brooder,  using  overhead  heat  and  a  chimney  of  fixed  length.  The  counter 
balance  at  the  top  of  the  picture  is  used  to  adjust  the  height  of  the  hover 
from  the  floor.  Note  that  the  curtain  is  several  inches  above  the  floor,  thus 
allowing  ample  brooder  ventilation. 


Fig.  6. — A  non-glowing  or  convection  type  electric  brooder,  using  overhead 
heat  and  a  chimney  of  fixed  length.  Note  the  use  of  good  electric  wiring 
practices.  The  hover  is  well  insulated  against  heat  losses<  especially  in  the 
central  section. 


12  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Sketch  No.  4  (fig.  3)  shows  the  usual  hover  employing  overhead 
non-glowing  elements,  with  the  addition  of  an  air  duct  in  the  floor  of 
the  brooder.  The  purpose  of  this  air  duct  is  to  permit  an  upward 
flow  of  fresh  air  through  the  floor  into  the  brooder,  thereby  forcing 
impure  air  out  under  the  curtain.  This  duct  alone  does  not  create  a 
positive  air  flow  and  may  or  may  not  produce  satisfactory  ventilation. 
This  type  is  shown  in  greater  detail  in  figure  7. 

Sketch  No.  5  (fig.  3)  shows  the  usual  hover,  employing  overhead 
non-glowing  elements  and  equipped  with  a  false  floor  made  of  laths 
tacked  to  1%  incn  by  3%  inch  joists  and  covered  with  burlap.  The 
purpose  of  this  false  floor  is  to  increase  the  effective  drying  surface, 
since  the  two  sides  of  the  burlap  and  the  lath  are  exposed  to  the  air 
flow ;  and  to  make  possible  the  removal  of  some  moisture  by  a  change 
of  burlap.  The  ventilation  of  the  brooder  is  not  affected  to  any 
noticeable  degree. 

Sketch  No.  6  (fig.  3)  shows  a  heating  element  installed  in  the 
brooder  floor  air  duct  to  induce  a  positive,  upward  flow  of  fresh 
air  into  the  brooder,  thus  forcing  the  impure  air  out  under  the  curtain. 
This  heating  element  is  usually  of  the  glowing  type  and  operates  at 
one-half  its  rated  voltage  or  one-fourth  of  its  rated  watts.  It  is  con- 
trolled by  a  separate  snap  switch  and  is  on  continuously.  The  main 
heat  source  is  still  the  overhead,  non-glowing  type  of  unit  shown  in 
sketch  No.  4,  fig.  3.  During  the  warm  part  of  the  day  this  over- 
head heat  can  be  cut  off  and  the  air  duct  element  left  to  supply  all 
necessary  heat  to  the  chicks.  Moisture  troubles  may  develop  only 
under  adverse  weather  conditions,  when  feeding  heavily  of  milk  or 
when  crowding  is  practiced.  Moisture  troubles,  in  this  instance,  may 
be  due  to  inadequate  ventilation  or  insufficient  heat  to  supply  the 
necessary  heat  of  vaporization. 

Sketch  No.  7  (fig.  3)  shows  the  usual  hover  employing  overhead, 
non-glowing  elements  and  equipped  with  a  heated  brooder  floor  but 
using  no  floor  air  duct.  Heat  is  transferred  by  conduction  from  the 
lower  to  the  upper  surface  of  the  floor,  where  convection  currents 
are  created,  which  tend  to  increase  the  air  movements  within  the 
brooder.  The  use  of  a  low  hanging  curtain  restricts  the  air  flow  and 
prevents  adequate  brooder  ventilation  unless  the  hover  is  raised.  The 
floor  temperature  did  not  exceed  80°  P  during  the  tests  of  this  type 
of  brooder. 


Bul.  441] 


THE   ELECTRIC    BROODER 


13 


Galvanized  Iron  Hover 
Heat  Insulation 


Perec  fain  Insulators 
Qead 


I 


Power  Leeds 

Thermostat  Snitch 

Stiver  Breaker 

Points 

Curtain 


PLAN 
Looking  Up  Prom  Beneath  Hover 

THE  ELECTRIC   POULTRY  BROODER 

USING 

A  LOW  GALVANIZED  IRON  HOVER ,SOME  NEAT  INSULATION,  BLACK 

OVERHEAD  HEATING  ELEMENTS,  A  THERMOSTAT  SWITCH,  CENTER 

FLOOR  AIR  DUCT  A  NO  CURTAIN. 

VENTILATION:  UNCONTROLLED  AND  SPASMODIC. 

GENERAL  DIRECTION  OF  AIR  FLOW:  IN  THRU 

AIR  DUC  T  OUT  UNDER  CURTAIN. 


Fig.  7. — Detail  of  line  sketch  4,  figure  3. 


16 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Sketch  10  (fig.  4)  shows  a  type  which  consists  of  a  low  flat  box 
about  ten  inches  high  (outside  measurement),  closed  on  three  sides, 
with  a  curtain  in  front.  The  heating  elements  are  located  in  a 
separate  side  chamber.  The  heating  chamber  connects  with*  the 
brooder  room  or  outside  air  from  below  and  with  the  brooder  air 
from  above,  the  convection  currents  being  led  up  past  the  heating 
elements,  over  a  partition,  down  across  the  brooder,  and  out  under 
the  curtain.  The  ventilation  effect  is  quite  positive  because  of  the 
thermal  head  developed.  From  the  standpoint  of  positive  brooder 
ventilation,  types  6,  8  and  10  have  definite  advantages. 


Fig.    10. — An   electric   brooder   using   black   overhead   heating    elements, 
thermostat  switch,  floor  air  ducts,  curtain,  and  heated  brooder  floor. 


Fig.  11. — A  simple,  homemade,  non-glowing  or  convection  type  of  electric 
brooder.  The  hover  resting  upon  its  legs  with  heating  compartment,  fresh  air 
duct,  heating  elements,  and  lid  removed  to  show  construction.  The  heating 
elements  are  in  series  each  operating  at  one-third  the  rated  voltage. 


Bul.  441] 


THE   ELECTRIC;    BROODER 


17 


Other  modifications  in  the  convection  type  of  brooder  exist,  which 
have  not  been  described  and  for  which  no  data  were  taken.  As 
illustrations,  figures  11,  12  and  13  are  included. 


Fig.  12. — Back  view  of  a  homemade  rectangular  box  type,  convection, 
electric  brooder.  The  brooder  is  closed  on  three  sides  with  a  curtain  in  front. 
The  air  enters  the  heating  compartment  through  two  air  ducts  (foreground,  at 
lower  edge),  moves  upward  past  heating  elements,  over  a  partition,  and  out 
under  the  curtain. 


Fig.  13. — Bottom  view  of  a  homemade  brooder  floor  sometimes  used  as  an 
auxiliary  to  insure  dry  hover  conditions. 


18  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


SPECIFICATIONS    OF     NON-GLOWING      (BLACK     HEAT)      ELECTRIC 

BROODERS 

While  the  following  list  of  parts  does  not  include  every  item  of 
which  a  brooder  is  made,  it  does  include  the  essentials  for  the  manu- 
facture of  an  electric  brooder  of  the  "black  heat,"  non-glowing,  or 
convection  type: 

1.  A  rather  flat  hover  to  cover  the  chicks  and  help  retain  the  heat. 
It  can  be  made  of  galvanized  iron,  lumber,  or  other  materials  as 
desired,  care  being  taken  to  select  a  material  which  will  not  be  injured 
by  the  pecking  of  the  chicks  and  which  is  easily  cleaned  and  sprayed. 
If  galvanized  iron  is  selected,  the  hover  should  be  conical  in  shape 
and  should  be  about  fifteen  inches  in  height.  It  should  have  at  least 
three  legs  about  six  inches  long  to  support  it  and  a  hook  at  the  top  to 
suspend  it  when  necessary.  A  %6-inch  iron  rod  should  be  rolled  into 
the  outer  edge  to  form  a  bead  and  give  rigidity.  If  of  wood,  it  can 
best  be  made  square  or  rectangular  in  shape  and  should  be  about  ten 
inches  high.  About  seven  square  inches  of  floor  space  per  chick 
should  be  allowed  in  designing  a  hover  of  any  type.  (See  brooder 
computations,  page  31  for  chick  capacity  determinations.) 

2.  Heat  insulation  of  the  hover  can  be  in  the  form  of  a  suitable 
insulating  material  applied  directly  to  the  hover  surfaces,  or  of  a 
hover  jacket  filled  with  air  or  other  insulating  material.  If  the  hover 
is  constructed  of  metal,  heat  insulation  is  a  very  important  item. 

3.  A  curtain  of  cloth  which  will  not  ravel. 

4.  For  electric  insulators,  porcelain  cleats  or  knobs  should  be  used 
every  six  or  eight  inches  for  fastening  heating  elements  to  the  hover 
(never  use  uninsulated  hooks  or  nails)  ;  porcelain  tubes  or  flexible 
asbestos  tubing,  wherever  electric  wires  pass  through  wood  or  metal ; 
and  fiber  board  or  similar  material  under  the  thermostat  and  other 
switches. 

5.  A  set  of  electric  heating  elements,  preferably  of  the  non-glowing 
type.  (See  table  2,  page  32  for  resistance  wire  sizes  and  lengths. 
Page  31  for  sample  brooder  design.) 

6.  A  thermostat  switch  in  the  electric  circuit  to  turn  heat  on  or  off 
automatically  as  required.  A  good  type  of  ether  wafer  or  bimetalic 
thermostat  is  recommended. 

7.  A  pilot  light  may  or  may  not  be  included.  Its  only  function  is 
to  indicate  if  the  power  is  on  or  off  and  if  the  thermostat  switch  is 
working  properly. 


BuL.  441]  THE   ELECTRIC    BROODER  19 

8.  A  good  ventilation  system  to  supply  fresh  air  and  to  remove 
water  vapor  and  other  impurities  from  the  brooder. 

9.  Necessary  rubber  or  asbestos-covered  copper  wire  of  correct  size 
for  the  load  to  be  carried.  (See  page  33  for  wire  size  calculations 
and  table  1  for  wire  characteristics.) 

Non-glowing  or  convection  brooders  were  found  in  the  field  in 
various  sizes.  In  the  square  or  rectangular  type  they  varied  from 
30  inches  by  30  inches  to  42  inches  by  70  inches,  and  in  the  round 
type  from  40  inches  to  72  inches  in  diameter. 


OPERATION  OF  NON-GLOWING   BROODERS 

The  action  of  this  type  of  brooder  in  its  most  common  form  is  as 
follows :  When  the  switch  is  closed  the  voltage  of  the  electric  system 
forces  a  current  of  electricity  through  the  heating  circuit.  The  heating 
elements  in  this  circuit  are  made  of  a  wire  which  offers  considerable 
resistance  to  the  current  flow  and  heat  is  generated.  The  amount  of 
heat  generated  varies  directly  as  the  product  of  the  square  of  the 
current  and  the  first  power  of  the  resistance  or  in  symbols  H  =  K  I2R 
where  H  is  the  heat  generated,  I  the  current  flowing  in  amperes,  R  the 
resistance  in  ohms  and  K  a  constant,  its  value  depending  upon  the 
system  of  heat  units  employed.  The  air  within  the  brooder  becomes 
heated  by  contact  with  the  heating  elements  or  by  radiation  from 
them,  causing  the  air  to  expand  and  move  upward  and  usually  out- 
ward, while  fresh  and  cooler  air  takes  its  place.  As  it  moves  away 
from  the  heating  elements  the  air  cools,  contracts  in  volume,  and 
gradually  settles  toward  the  floor.  A  part  of  this  air  in  time  passes 
out  under  the  curtains  and  a  part  returns  to  the  heating  elements  to 
repeat  its  journey.  If  the  heat  furnished  is  adequate  and  the  air 
paths  through  the  brooder  are  not  too  completely  restricted,  the 
resulting  convection  currents  set  up  succeed  in  accomplishing  brooder 
ventilation. 

The  temperature  within  the  brooder  continues  to  rise  until  the 
thermostat  switch  interrupts  the  circuit.  When  the  air  of  the  brooder 
cools  again  to  a  certain  temperature,  the  thermostat  switch  closes  and 
electric  heating  is  resumed. 

The  use  of  curtains,  insulation  and  thermostat  switches  all  tend 
to  reduce  heating  costs.  Curtains,  however,  interfere  with  ventilation 
and  when  used  some  provision  should  be  made  to  maintain  adequate 
air  replacement. 


20  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

Every  chick  throws  off  water  vapor  from  its  lungs  and  in  its  feces, 
the  amount  depending  first,  upon  its  size  or  age,  second,  upon  the 
kind  of  food,  and  third,  upon  the  weather  conditions,  "While  the 
chicks  are  active  about  the  brooder  room  and  runway,  the  droppings 
are  scattered  so  that  their  moisture  content  can  be  absorbed  and 
removed  by  the  room  ventilation.  However,  at  night  when  they  enter 
the  hover,  the  chicks  concentrate  within  a  small  and  often  poorly 
ventilated  space  yet  the  amount  of  water  given  off  by  lung  and  feces 
and  which  must  be  dissipated  remains  practically  the  same.  Curtains 
tend  to  prevent  the  dissipation  of  this  moisture  into  the  room  or  out- 
side air  and,  as  a  result,  the  humidity  of  the  brooder  air  may  rise. 
The  temperature  of  the  hover  tends  to  increase  also  because  of  the 
heat  given  off  by  the  sleeping  chick,  and  soon  reaches  a  point  at  which 
the  thermostat  switch  opens  and  the  electric  heat  is  cut  off.  With  the 
heat  cut  off,  ventilation  is  impaired,  the  air  soon  becomes  saturated 
and  a  condition  usually  called  "sweating"  follows.  "Sweating"  on 
a  chick's  feathers  or  upon  a  window  pane  in  a  warm  room  is  due 
solely  to  the  condensation  of  water  from  the  saturated  warm  air  upon 
cooler  surfaces.  The  condensation  from  the  outside  air  upon  the 
cooler  roof  of  a  house  might  have  been  called  "sweating"  instead  of 
dew.  The  remedy  for  sweating  then  is  adequate  heat  to  cause  the 
moisture  deposits  to  vaporize  and  frequent  enough  brooder  air  changes 
to  remove  this  vapor.  Adequate  ventilation  or  adequate  heat  alone 
cannot  economically  accomplish  the  result.  The  two  must  work 
together. 


GLOWING   OR   "RADIANT"?  TYPES  OF   BROODERS   STUDIED 

Some  brooders  make  use  of  the  heat  radiated  from  glowing  wires 
to  warm  the  space  occupied  by  the  chicks.  They  are  usually  conical  in 
shape  with  the  elements  located  near  the  apex.  Heat  reflectors  are 
used  to  increase  the  effect  of  the  heating  elements,  and  some  kind  of 
insulating  material  is  used  on  the  surface  of  the  metal  of  the  hover  to 
reduce  heat  loss  to  a  minimum.     (See  sketches  11  and  12,  fig.  4.) 


.  .  7  Qbjects  begin  to  glow,  that  is  emit  light  which  the  eye  is  able  to  detect, 
at  approximately  400°  C  (752°  F).  Up  to  the  point  at  which  they  begin  to 
glow  they  retain  their  natural  color,  which  is  due  entirely  to  reflected  light. 
The  color  first  noted  as  metals  begin  to  glow  is  a  dull  red,  which  gradually 
brightens  as  the  temperature  increases  through  blood  red,  cherry,  bright  red, 
salmon,  orange,  lemon,  light  yellow,  and  white.  It  should  be  remembered  that 
this  color  is  due  to  no  chemical  change  in  the  metal  but  to  the  effect  of  the 
waves  of  the  radiated  light  upon  the  eye. 


Bul.  441] 


THE   ELECTRIC    BROODER 


21 


Fig.  14. — A  conical  galvanized  iron  "radiant"  or  glowing  type  of  electric 
brooder^  which  uses  glowing  heating  elements  and  a  right  vertical  cone  heat 
reflector.  Note  the  absence  of  a  curtain.  The  heating  elements  are  located 
just  below  the  heat  reflector  in  the  apex  of  the  cone.  By  raising  the  hover 
slightly  and  placing  the  roosts  in  this  heated  area  as  shown,  the  chicks  can  be 
easily  taught  to  go  to  roost. 


Fig.  15. — A  concave  cone  heat  reflector  sometimes  used  in  "radiant"  or 
glowing  type  brooders.  A  concave  reflector  concentrates  the  heat  rays  toward 
the  center  tending  to  create  a  "hot  spot"  on  the  floor. 


22  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

The  glowing  elements  used  as  the  heat  source  in  these  brooders 
radiate  heat  outward  in  all  directions.  Since  the  chicks  can  be  on  the 
under  side  only,  the  heat  radiating  upward  would  be  of  no  benefit  to 
them  if  not  reflected.  The  heat  reflector,  then,  plays  a  very  important 
part  in  this  type  of  brooder.  Concave  and  cone  reflectors  concentrate 
the  rays  toward  the  center,  causing  a  ' '  hot  spot "  to  be  formed  on  the 
brooder  floor.  By  some,  this  is  considered  waste  floor  space,  since  the 
heat  is  too  intense  for  the  chicks  to  remain  in  this  area.  It  has  the 
virtue,  however,  of  preventing  center  crowding  and  allows  a  warmer 
portion  of  the  brooder  for  those  chicks  requiring  more  heat.  Also, 
when  a  ' '  hot  spot ' '  is  used,  a  larger  floor  area  may  be  available,  since 
the  heat  may  extend  out  beyond  the  confines  of  the  hover,  sometimes  to 
a  distance  of  eight  or  ten  inches,  and  chicks  have  frequently  been 
observed  resting  comfortably  in  this  area. 

The  intensity  and  size  of 'this  "hot  spot"  can  be  controlled  by  the 
height  of  the  reflector  from  the  floor,  by  the  radius  of  curvature  of  the 
reflector  by  lowering  the  wire  surface  temperature,  or  by  screening 
the  rays.  Taking  advantage  of  these  principles,  recent  models  have 
adopted  improved  types  of  heat  reflectors  (see  heat  reflectors,  page 
10),  and  at  least  a  part  of  the  heat  is  being  controlled  by  a  thermostat 
switch.  Sketch  13  of  figure  4  shows  the  usual  radiant  brooder 
equipped  with  a  flat  reflector.  Since  the  angle  at  which  the  heat  rays 
leave  the  reflector  must  equal  the  angle  at  which  they  strike,  this 
reflector  diffuses  the  rays  to  some  extent.  The  temperature  at  the 
center  of  the  hot  spot  is  thus  decreased  slightly  and  its  area  increased, 
due  to  this  diffusion. 

Sketch  14  (fig.  4)  shows  the  usual  radiant  brooder  equipped  with 
a  convex  heat  reflector.  A  convex  reflector  of  small  radius  diffuses 
the  rays  very  rapidly,  while  one  of  greater  radius  diffuses  to  a  less 
degree.  The  radius  of  curvature  should  not  be  less  than  20  inches 
when  a  hover  having  a  ratio  of  height  to  diameter  of  1  to  2  is  used. 

Sketch  15  (fig.  4)  shows  the  usual  radiant  brooder  equipped  with 
an  inverted  right  cone  reflector.  With  this  reflector  a  good  many  of 
the  heat  rays  must  suffer  double  reflection,  and  some  will  be  converted 
into  heat  before  they  reach  the  floor.  If  this  type  is  used,  the  height 
of  the  reflector  or  cone  should  be  about  one-fifth  of  the  reflector 
diameter.  The  resulting  diffusion  of  the  rays  then  approaches  that 
of  the  convex  reflector  of  large  radius  as  described  under  No.  14. 
Since  a  cone  is  easily  formed,  this  reflector  will  be  very  popular,  but 
care  should  be  taken  to  construct  it  with  proper  dimensions. 


Bul.  441] 


THE    ELECTRIC    BROODER 


23 


Fig.  16. — A  conical,  galvanized  iron,  il radiant"  or  glowing  type  of  electric 
brooder,  which  uses  radiant  heating  elements  and  a  convex  copper  heat  reflector. 
Note  the  heavy  bead  at  the  edge  which  gives  the  hover  rigidity,  short  legs 
(not  over  three  inches),  thermostat  switch  and  observation  door  on  the  side. 
The  hover  height  should  be  about  one-half  the  diameter. 


Fig.  17. — A  convex  copper  heat  reflector  such  as  that  used  in  the  radiant 
electric  brooder.  Two  heating  elements  are  on  the  thermostat  circuit  and  two 
are  controlled  by  a  separate  switch.  This  type  of  reflector  diffuses  the  heat 
rays,  making  the  complete  area  under  the  hover  habitable  by  the  chick. 


24 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


Fig.  18. — A  conical,  galvanized  iron,  "convection"  and  "radiant"  brooder, 
using  electric  heat.  The  heating  elements  are  cast  in  concrete  and  have  taps 
for  110  or  220-volt  service.  The  concrete  block  is  hollow  at  the  center  and 
this  hollow  center  compartment  is  connected  to  the  room  air  by  an  air  duct 
at  the  bottom.  The  air  in  the  center  compartment  becomes  heated  and  rises, 
while  new  and  cooler  air  takes  its  place  via  the  duct.  The  concrete  when 
heated  radiates  heat  into  the  brooder.  It  therefore  combines  the  characteristics 
of  both  the  convection  and  the  radiant  brooders. 


Fig.  19. — A  conical,  galvanized  iron,  convection  type  of  hover,  which  uses 
combination  top  and  center  heat. 

a.  The  hover  resting  upon  its  legs,  with  the  center  intake  opening  of  the 
air  duct  showing  at  the  right. 

h.  The  hover  resting  on  its  side  showing  the  center  heating  compartment, 
air  duet,  reflector^  top  heating  circuit,  porclain  knob  insulators,  and  ether  wafer 
thermostat.  Some  heat  is  radiated  from  this  center  compartment  into  the 
brooder  and  some  is  reflected  downward  from  the  reflector  above. 


Bul.  441] 


THE   ELECTRIC    BROODER 


25 


Power  Leads  from   Trans 
Mas  ter  Switch     and    Mam 

Fuse  B/ocx, 

[Leads  shou/d  be  largo 

Jo  carry  mofimum  lead 

Heating) 


Farm  Power  B> 
(Use  heavy  Copper.) 


Form  fbk/e  r   Circuits 
/f**,  1,2,3,4,.  etc 


Circuit  At'21  /lojter  Fuses. 
(Fuse  a/  about  12f  %  of  Full  Lead., 


-Master  Fuses, 
(fuse  at  about  lSb%  of 
Fut/  LoadXOpen  Main 
Switch  before  fusing  or  Horn- 
ing on  Farm  Fouler  Bus) 


H//o  -  rvaft  Hour  Me  ter 
(Usually  Power  Company 
Property) 


Fig.  20. — Electric  wiring  diagram  of  a  typical  farm  power  layout  showing  an 
electric  brooder  connected  to  one  of  the  available  power  circuits. 


26  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

The  reflector  should  be  made  of  some  metal  which  will  not  curl 
or  warp  when  subjected  to  the  heat  from  the  elements.  Tin  does  very 
well  and  when  it  tarnishes  can  be  given  a  coat  of  high  heat-resistant 
aluminum  paint.  This  paint  costs  very  little  and  increases  the 
reflector  efficiency  to  approximately  80  per  cent.  Copper,  brass,  zinc, 
or  other  metals  can  be  used  but  are  more  expensive.  Galvanized  iron 
should  not  be  used  since  the  heat  causes  the  zinc  coating  to  peel  off 
after  a  short  time. 

Sketch  16  (fig.  4)  shows  a  radiant  brooder  equipped  with  a  com- 
bination convex  and  concave  reflector.  The  center  portion  diffuses 
the  heat  rays  and  the  concave  rim  prevents  the  formation  of  a  radia- 
tion heat  pocket,  where  the  reflector  meets  the  hover  sides.  It  should 
be  remembered  in  the  construction  of  this  reflector  that  for  best  results 
the  hover  sides  should  meet  the  concave  rim  at  a  tangent  and  that  no 
seams,  wrinkles  or  rough  spots  should  exist  on  the  reflecting  surface. 
A  hover  2^2  feet  by  5  feet  would  require  a  convex  reflector  about  20 
inches  in  diameter  located  26  inches  above  the  floor.  If  the  surface 
has  a  curvature  of  approximately  26  inches  the  heat  rays  will  be 
reflected  uniformly  to  the  floor. 


SPECIFICATIONS  OF  GLOWING  OR   RADIANT  TYPE   BROODERS 

The  main  parts  to  the  glowing  type  of  brooder  are : 

1.  A  conical,  galvanized  iron  hover  to  cover  the  chicks  and  help 
retain  the  artificial  heat.  It  should  have  a  hook  at  the  top  to  suspend 
it,  at  least  three  legs  (about  three  inches  long)  to  support  it,  and  a 
%6-ineh  rod  rolled  into  the  edge  to  form  a  bead  and  to  give  rigidity. 
Short  legs  are  specified  so  as  to  permit  the  lowering  of  the  hover  while 
the  chicks  are  young  or  when  power  fails.  The  ratio  of  hover  height 
to  diameter  should  be  about  1  to  2. 

2.  A  heat  reflector,  preferably  that  shown  under  sketch  No.  16 
(fig.  4)  with  dimensions  approximately  as  listed  on  page  22. 

3.  Adequate  heat  insulation  of  the  hover.  This  may  be  applied 
directly  to  the  hover  surfaces,  or  may  consist  of  a  hover  jacket  filled 
with  air  or  other  insulating  material. 

4.  Electric  insulators  for  wiring  and  fixtures.  Porcelain  tubes  or 
bushings  should  be  used  wherever  the  wires  pass  through  the  hover 
metal ;  porcelain  base,  screw  sockets,  or  insulated  clips,  where  the 
elements  are  attached  to  the  reflector  and  fiber  board  or  similar 
material  under  the  thermostat  switch  and  other  switches. 


BUL.  441]  THE   ELECTRIC    BROODER  27 

5.  Electric  service  connections.  Screw  sockets  or  spring  connector 
clips  should  be  used  that  will  carry  at  least  twenty  amperes  without 
heating. 

6.  Glowing  type  of  electric  heating  elements.  Two  or  more  units 
should  be  used  with  a  total  wattage  equal  to  the  brooder  demand. 
(For  brooder  calculations  see  page  31  and  for  resistance  wire  size 
and  length,  see  table  2.) 

7.  A  thermostat  sivitch,  preferably  of  the  expanding  ether  wafer 
or  bimetalic  type  for  temperature  control,  to  be  connected  into  one 
of  the  heating  circuits.     (Not  all  the  circuits.)     See  figure  20. 

8.  Separate  wall  switches  for  each  heater  circuit.  (Three  heating 
elements  will  require  three  wall  switches  in  addition  to  the  thermostat 
switch,  for  ease  in  control.) 

9.  Necessary  rubber  covered  copper  wire  to  bring  the  power  from 
the  supply  mains  to  the  hover.  It  should  be  of  correct  size  for  the 
load  to  be  carried.  (For  wire  size  calculations,  see  pages  33  and  35, 
and  for  wire  characteristics,  see  table  1.) 

10.  Necessary  asbestos  covered  copper  wire  to  connect  the  heating 
elements  under  the  hover  to  the  rubber  covered  leads  above  the  hover. 
Asbestos  covered  leads  should  be  used  wherever  the  wires  are  subjected 
to  the  hover  heat. 

"Radiant"  brooders  were  found  in  various  sizes,  from  42  to  72 
inches  in  diameter.  There  is  no  reason  why  smaller  units  could  not  be 
used  but  heating  costs  per-chick-season  increase  as  the  number  of 
chicks  per  brooder  decreases.  Again,  as  in  the  convection  brooder,  the 
five-foot  size  was  the  one  found  to  be  most  commonly  used. 


OPERATION    OF    GLOWING    TYPE    BROODERS 

As  in  the  non-glowing  brooder,  the  heat  in  the  glowing  type  is 
developed  by  an  electric  current  flowing  through  heating  elements, 
the  length,  size,  and  material  of  which  are  such  as  to  cause  them  to 
glow.  The  main  heat  transfer  is  by  radiation  but  a  slight  convection 
effect  results  where  the  air  comes  in  direct  contact  with  the  heating 
elements. 

That  portion  of  the  heat  which  is  generated  on  the  under  side  of 
the  heating  element  is  radiated  directly  to  the  floor,  but  all  heat 
appearing  on  the  upper  side  must  be  reflected.  This  amounts  to 
approximately  one-half  of  the  total  heat.  It  does  not  become  useful 
until  the  rays  are  absorbed  by  the  chicks,  the  floor,  or  the  hover  walls. 


28 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


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Bul.  441]  THE   ELECTRIC    BROODER  29 

When  the  temperature  beneath  the  hover  rises  to  a  certain  point, 
the  thermostat  opens  one  circuit  of  the  heating-  system.  Should  the 
temperature  continue  to  rise,  a  wall  switch  on  one  of  the  other  heating 
circuits  may  be  opened  or  the  heat  allowed  to  find  its  own  balance, 
while  the  chicks,  if  necessary,  move  further  out.  The  radiant  heat 
applied  directly  to  the  floor  causes  any  moisture  deposits  to  evaporate 
into  the  air  and  pass  from  the  hover  into  the  room  air,  there  being 
no  curtain  to  restrict  the  flow.  This  automatic  removal  of  moisture 
by  the  radiant,  curtainless  brooder  is  an  important  advantage  when 
used  by  inexperienced  poultrymen.  Tests  indicate  that  with  proper 
heat  control  sufficient  heat  can  be  obtained  to  effect  proper  ventilation 
and  drying  without  excessive  additional  cost.  No  harmful  effects 
upon  the  chicks  from  the  light  of  the  glowing  elements  have  been 
reported  or  observed. 


COMBINATION   CONVECTION   AND    RADIANT   BROODERS 

Combinations  of  the  various  types  of  brooders  previously  described 
have  resulted  in  units  employing  both  types  of  heat  transfer.  This 
seems  to  be  a  logical  development,  since  such  a  brooder  may  be  able 
to  incorporate  most  of  the  advantages  of  both  types  and  still  remove 
some  of  their  disadvantages.  By  using  both  glowing  and  non-glowing 
elements  as  an  illustration,  the  radiant  element  could  be  smaller  than 
is  now  possible,  while  the  thermostat  could  be  installed  in  the  non- 
glowing  circuit  thus  furnishing  a  heat  "safety  factor"  and  removing 
the  objection  that  radiant  elements  burn  out  when  subjected  to 
thermostatic  action. 


ELECTRIC    BROODER    WIRING    PRACTICE 

The  following  suggestions  will  be  found  helpful  in  the  construction 
of  an  electric  brooder  and  its  connection  to  the  power  leads : 

1.  The  wire  should  be  of  the  correct  size  and  should  be  properly 
insulated  for  the  load  to  be  carried  and  the  temperatures  encountered. 
(For  wire  sizes  and  current  carrying  capacities,  see  table  1.) 

2.  The  heating  elements  should  develop  the  proper  amount  of  heat 
and  should  be  made  of  high  grade  resistance  wire.  (For  resistance 
wire,  sizes  and  lengths  necessary  to  develop  specified  power,  see 
table  4.) 

3.  The  brooder  power  circuit  should  be  properly  protected  by 
fuses.  (Fuses  should  not  be  used  with  a  rating  greater  than  125 
per  cent  of  full  load.) 


30 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION 


4.  The  thermostat  switch  should  be  of  sturdy  construction  and 
positive  in  operation.  The  breaker  points  should  be  of  silver  and  not 
less  than  three-sixteenths  of  an  inch  in  diameter  to  avoid  burning. 
A  condenser  across  tlie  breaker  points  reduces  the  intensity  of  the  arc. 

5.  The  service  connections  (sockets  or  spring  clips)  should  be 
heavy  enough  to  carry  the  current  at  the  temperature  encountered. 
This  is  very  important  on  account  of  the  high  air  temperatures  in 
which  they  may  operate. 

6.  All  poor  contacts,  such  as  loose  screws,  poorly  spliced  wires,  and 
badly  formed  eyes,  must  be  avoided. 

7.  Porcelain  or  other  good  insulators  should  be  used  at  frequent 
intervals  beneath  the  hover  and  where  the  leads  pass  through  the 
hover  material.  (Uninsulated  hooks  or  nails  should  never  be  used  to 
suspend  the  elements  from  the  hover.) 

8.  Only  high  grade  electrical  materials  should  be  used. 


TABLE  1 

Table  Giving  Resistance,  Weight,  Current  Carrying  Capacity,  and  Voltage 
Drop  for  Rubber  Covered  and  Weatherproof  Copper  Wire 


Resist- 

Rubber covered  copper  wire 

Weatherproof  copper  wire 

Wire 

ance  per 

Voltage 

Voltage 

size 

1000  ft. 

Weight 

Maximum 

drop  in 

Weight 

Maximum 

drop  in 

B&S 

at68°F., 

per 

Feet 

safe 

leads  per 

per 

Feet 

safe 

leads  per 

gage* 

or  20°  C 

1000  ft. 

of  wire 

current 

100-foot 

1000  ft. 

of  wire 

current 

100-foot 

including 

per 

carrying 

lengths 

including 

per 

carrying 

lengths 

wire  and 

pound 

capacity 

for 

wire  and 

pound 

capacity 

for 

insulation 

in 
amperes* 

maximum 
currentf 

insulation 

in 
amperes* 

maximum 
currentf 

18 

6.385 

14 

71.4 

3 

1.92 

16 

62.4 

5 

3.19 

16 

4.015 

18 

55.5 

6 

2.41 

20 

50.0 

10 

4.01 

14 

2.525 

30 

33  3 

15 

3.79 

25 

40.0 

20 

5.05 

12 

1.588 

41 

24.4 

20 

3.18 

35 

28.6 

25 

3.97 

10 

..9989 

55 

18.2 

25 

2.50 

53 

18.9 

30 

3.00 

8 

..6282 

76 

13.1 

35 

2.20 

75 

13.3 

50 

3.14 

6 

.3951 

134 

7.5 

50 

1.98 

112 

8.9 

70 

2.77 

5 

.3133 

190 

5.3 

55 

1.72 

135 

7.4 

80 

2.51 

4 

.2485 

220 

4  5 

70 

1.74 

164 

6.1 

90 

2.24 

3 

.1970 

270 

3.7 

80 

1.57 

199 

5.0 

100 

1.97 

2 

.1563 

320 

3.1 

90 

1  41 

260 

3.8 

125 

1.95 

1 

.1239 

365 

2.7 

100 

1.24 

316 

3.2 

150 

1.86 

0 

.0983 

495 

2.0 

125 

1.23 

407 

2.5 

200 

1.97 

00 

.0779 

600 

1.7 

150 

1.17 

502 

2.0 

225 

1.75 

000 

.0618 

760 

1.3 

175 

1.08 

629 

1.6 

275 

1.70 

0000 

.0490 

925 

1.1 

225 

1.10 

767 

1.3 

325 

1.59 

*From  1925  Electrical  Safety  Orders,  Industrial  Accident  Commission,  State  of  California, 
pages  26-27. 

fThe  wire  length  required  is  twice  the  distance  in  feet.  Thus,  15  amperes  carried  50  feet  to  a 
load  will  require  100  feet  of  No.  14  wire  and  will  cause  a  voltage  drop  of  3.79  volts. 


BUL.  441]  THE   ELECTRIC    BROODER  31 


COMPUTATIONS  ON  THE   SELECTION   AND   DESIGN   OF   AN 
ELECTRIC    BROODER 

In  order  to  illustrate  the  method  of  computing  hover  size  and 
wiring  specifications  let  it  be  required  to  design  a  "radiant"  or  glow- 
ing type  electric  brooder  of  500-chick8  capacity,  to  operate  on  a  110- 
volt  electric  circuit.    Allowing  7  sq.  in.  of  floor  space  per  chick,  then — 

Free  area  under  hover  =  500  X  7  =  3500  sq.  in.  or  24.3  sq.  ft. 

If  the  hover  is  to  be  circular  its  diameter  can  be  found  from  the 

formula  D  =  J  4  Area  •     The   diameter  then  =  J  4  X  24-3  =5.56 
>  3.1416  M    3.1416 

feet.  But  if  the  hover  is  to  be  square  the  length  of  one  side  can  be 

found  from  the  formula-length  of  side  =  VA= V  24lT=4.93  feet. 

The  size  of  the  heating  elements  should  next  be  determined 
and  assuming  2.5  watts  per  chick,  the  total  wattage  of  the  heating 
elements  =  500  X  2.5  =  1250  watts.9 

Let  it  be  assumed  now  that  three  separate  circuits  are  to  be  used. 
The  power  for  each  circuit  would  be  1250  -=-  3  =  416  watts,  and 
by  applying  the  formula  for  single  phase  non-inductive  electric  cir- 
cuits, Watts  =  Volts  X  Amperes,  the  current  through  each  heating 

416 
element  is  found  to  be  Current  =  -— -  =  3.78  amperes. 

Now  by  referring  to  table  2  it  will  be  found  that  No.  27  nickel 
chrome  wire  will  have  a  surface  temperature  of  approximately  1472°  F 
when  carrying  3.44  amperes  and  by  referring  to  figure  21  it  will  be 
seen  that  No.  28  wire,  slightly  smaller  than  No.  27,  begins  to  glow  at 
about  1150  degrees  F. 


s  The  Poultry  Husbandry  Division  of  the  University  of  California  recom- 
mends that  not  more  than  300  chicks  be  placed  in  any  brooder  at  one  time. 
This  design  is  carried  through  for  a  brooder  of  500-chick  capacity  because  it 
illustrates  design  features  better  and  because  the  average  brood  found  in  the 
field  during  these  tests  was  slightly  above  this  figure. 

9  One  thousand  watts  of  electrical  power  applied  for  one  hour  will  produce 
a  heating  effect  equal  to  approximately  3412  British  thermal  units  (B.t.u.)  or 
800.5  kilogram-calories  (kg-cal.).  Therefore,  1  watt-hour  will  produce  3.412 
B.t.u.  or  .8005  kilogram-calories.  A  600-watt  element  operating  for  one  hour 
will  then  produce  GOO  X  3.412  B.t.u.  =  2047.2  B.t.u.,  or  600  X  .8605  kg-cal.  = 
516.3  kilogram-calories.  1  B.t.u.  is  equivalent  to  .252  kilogram-calories  and 
1  kilogram-calorie  is  equivalent  to  3.965  B.t.u.  The  kilogram-calorie  is  gen- 
erally defined  as  the  amount  of  heat  required  to  raise  one  kilogram  of  water 
from  14.5°  C  to  15.5°  C.  The  British  thermal  unit  is  that  quantity  of  heat 
used  in  raising  the  temperature  of  one  pound  of  water  from  62°  F  to  63°  F. 


32 


UNIVERSITY    OP    CALIFORNIA EXPERIMENT    STATION 


After  selecting  the  wire  to  be  used  it  is  next  necessary  to  determine 

the  length.  This  can  be  found  by  knowing  that  the  Length  required  = 

Total  Resistance         m  .,     _     .         L.  .  J  „  ,T 

=r — 7— = — .     Table  2  gives  the  resistance  of  No.  27  wire  as 

Resistance  per  foot 

3.274  ohms  per  foot  at  68°  F  or  3.274  X  1.1122    (resistance  factor, 

see  table  3)  =3.6413  ohms  per  foot  at  1472°  F. 

It  is  also  known  that  Volts  =  Amperes  X  Resistance  and  in  this 

case  the  voltage  =  110  and  amperage  =  3.79.    Therefore 

110  ■ ,  ,  .,     ,.        .,      .  „..  29 


Resistance 


29  ohms  and  the  Length  of  Wire  = 


7.97 
feet. 


3.79  —*».  -,  3  6413 

The  safe  carrying  capacities  of  various  size  wires  are  given  in 
table  1  and  the  computations  for  the  service  wires  are  similar  to  those 
for  the  heating  elements. 


TABLE  2 

Eesistance,    Current,    and    Temperature    Characteristics    of    "Nichrome" 

Eesistance  Wire,  with  Specific  Eesistance  of  600  OHMS.t 

Per  Circular,  Mil  Foot  at  68°  F(20°  C) 


Wire 
size 

Diame- 
ter of 
wire  in 
inches 

Resist- 
ance in 

ohms 
per  foot 
at  68°  F. 

20°  C. 

Current  in  amperes  necessary  to  produce  the  temperatures  listed  below 
for  straight  wire  in  air,  in  a  horizontal  position 

B.&S. 
gage 

212°  F. 
100°  C. 

392°  F. 
200°  C. 

572°  F. 
300°  C. 

752°  F. 
400°  C. 

932°  F. 
500°  C. 

1112°  F. 
600°  C. 

1292°  F. 
700°  C. 

1472°  F. 
800°  C. 

1652°  F. 
900°  C. 

No.  10 

.102 

.063 

12.3 

22.4 

30.6 

38.0 

44.8 

51.2 

57.0 

63.1 

68.8 

No.  12 

.081 

.100 

8.80 

16.1 

22.0 

27.3 

32.1 

36.8 

40.8 

45.3 

49.4 

No.  14 

.064 

.161 

6  31 

11.5 

15.8 

19.6 

23.0 

26.2 

29.3 

32.4 

35.5 

No.  16 

.051 

.254 

4  54 

8.28 

11.35 

14.1 

16.5 

18.9 

21.0 

23.4 

25.6 

No.  18 

.040 

.412 

3.26 

5.95 

8.13 

10.1 

11.8 

13.6 

15.1 

16.8 

18.4 

No.  20 

.032 

.645 

2.32 

4.27 

5.83 

7.30 

8.53 

9.70 

10.85 

12.0 

13.2 

No.  21 

.0285 

.813 

1.97 

3.62 

4.94 

6.17 

7.23 

8.21 

9.20 

10.2 

11  2 

No.  22 

.0254 

1.031 

1.67 

3.07 

4.18 

5.23 

6.13 

6.96 

7.80 

8.65 

9.46 

No.  23 

.0226 

1.292 

1.42 

2.60 

3.54 

4.43 

5.19 

5.90 

6.61 

7.33 

8.02 

No.  24 

.0201 

1.634 

1.20 

2.20 

3.00 

3.75 

4.40 

5.00 

5.60 

6.20 

6.80 

No.  25 

.0179 

2.060 

1.02 

1.86 

2.54 

3.18 

3.73 

4.25 

4.67 

5.27 

5.76 

No.  26 

.0159 

2.611 

.865 

1.58 

2.15 

2.70 

3.16 

3.61 

3.96 

4.47 

4.88 

No.  27 

.0142 

3.274 

.734 

1.34 

1.82 

2.28 

2.68 

3.06 

3.36 

3.80 

4.13 

No.  28 

.0126 

4.159 

.622 

1.13 

1.54 

1.85 

2.27 

2.62 

2.86 

3.23 

3.50 

No.  29 

.0113 

5.168 

.527 

.960 

1.305 

1.57 

1.93 

2.22 

2.45 

2.71 

2.97 

No.  30 

.0100 

6.600 

.447 

.814 

1.105 

1.33 

1.64 

1.89 

2.08 

2.30 

2.52 

No.  31 

.0089 

8.333 

.378 

.680 

.935 

1.13 

1.39 

1.60 

1.77 

1.95 

2.14 

No.  32 

.0080 

10.313 

.321 

.577 

.791 

.955 

1.18 

1.36 

1.50 

1.66 

1.81 

No.  33 

.0071 

13.098 

.272 

.490 

.670 

.809 

1.00 

1.15 

1.28 

1.41 

1.53 

No.  34 

.0063 

16.623 

.231 

.416 

.567 

.685 

.849 

.980 

1.06 

1.18 

1.29 

No.  35 

.0056 

21.019 

.196 

.353 

.480 

.580 

.720 

.830 

.90 

1.00 

1.09 

No.  36 

.0050 

26.400 

.166 

.300 

.406 

.491 

.611 

.704 

.765 

.850 

.924 

No.  37 

.0045 

32.672 

.141 

.254 

.344 

.416 

.518 

.597 

.650 

.721 

.783 

No.  38 

.0040 

41.240 

.120 

.216 

.291 

.352 

.440 

.507 

.552 

.613 

.663 

No.  39 

.0035 

54.098 

.101 

.183 

.246 

.298 

.373 

.430 

.467 

.517 

.566 

No.  40 

.0031 

73.333 

.085 

.155 

.208 

.252 

.316 

.364 

.396 

.439 

.480 

lengths. 


Adapted  from  tables  by  Driver-Harris  Company,  Detroit,  Michigan, 
tlf  a  wire  of  different  specific  resistance  is  used,  see  illustrative  problem,  page  33,  for  correct 


Bul.  441 


THE    ELECTRIC    BROODER 


33 


TABLE  3 

"Color-Temperature"  Chart  tor  Metals  and  "Temperature  Correction 
Factor"  for  "Nichrome"  Resistance  Wire  at  Temperatures  Above 
68°   F.     An  Approximate  " Color-Temperature"  Chart  for  all  Metals. 

Part  "A" 


Color  of  metal 

Black  or 
natural 

Faint 
red 

Blood 
red 

Cherry 
red 

Bright 
red 

Salmon 
red 

Orange 

Lemon 

Light 
yellow 

White 

Approximate 
temperature 

Zero  to 
800°  F 

800°  F 

to 
1050°  F 

1050°  F 
to 

1150°  F 

1150°  F 

to 
1300°  F 

1300°  F 

to 
1600°  F 

1600°  F 

to 
1700°  F 

1700°  F 

to 
1800°  F 

1800°  F 

to 
1950°  F 

1950°  F 

to 
2050°  F 

2050°  F 
and  up 

"Temperature  Correction  Factor "t  for  the  Resistance  Wire.  Used  in 
these  Tables,  Specific  Resistance  660  Ohms  per  Circular  Mil  Foot  at 
68°  F,  20°  C.     For  Straight  Wire  in  a  Horizontal  Position  in  Air. 

Part  "B" 


Wire  surface 

[68°F 

212°  F 

392°  F 

572°  F 

752°  F 

932°  F 

1112°  F 

1292°  F 

1472°  F 

1652°  F 

1832°  F 

temperature 

\ 

[20°C 

100°  C 

200°  C 

300°  C 

400°  C 

500°  C 

600°  C 

700°  C 

800°  C 

900°  C 

1000°  C 

Resistance  cor- 

rection factor. .. 

1.0000 

1.0185 

1.0417 

1.0645 

1.0828 

1.0928 

1.0960 

1 . 1022 

1.1122 

1.1257 

1 . 1423 

Adapted  from  tables  published  by  the  Driver-Harris  Company,  Detroit,  Michigan. 
•(•Illustration  on  use  of  "Part  B"  of  Table  3: 

Resistance  per  foot  of  No.  25  resistance  wire  at  68°  F.,  20°  C.  is  2.060  ohms.     (Table  2.) 
What  is  the  resistance  per  foot  of  this  wire  at  1472°  F.,  800°  C? 
Under  1472°  F.,  (800°  C.)  above,  find  1.1122  (Correction  factor). 

Therefore,  resistance  per  foot  of  No.  25  resistance  wire  at  1472°  F.  (800°  C.)  is  2.060X1.1122  = 
2.2911  ohms. 


Total  watts  to  be  delivered  by  the  service  wires  to  each  brooder  = 
1250  watts. 


Current  flowing  to  each  brooder  = 


1250 


11.36  amperes  and  from 


110 

table  1  it  is  seen  that  No.  16  rubber  covered  wire  will  carry  6  amperes 
safely  and  No.  14  will  carry  15  amperes.  It  is  better  to  be  amply  safe 
so  No.  14  should  be  chosen. 

If  a  wire  of  different  specific  resistance  than  that  of  table  2  is 
used,  its  length  can  be  obtained  by  multiplying  the  above  length 
(7.97)  by  660  and  dividing  by  the  new  specific  resistance;  or,  as  an 
illustration,  if  the  specific  resistance  per  circular  mil  foot  is  750 
instead  of  660  ohms,  the  correct  length  is  obtained  by  multiplying  the 

old  length,  7.97,  by  ^^-=7.02  feet.     (This  is  not  an  exact  solution 

but  for  practical  computations  will  be  found  entirely  satisfactory.) 


34 


UNIVERSITY    OP    CALIFORNIA EXPERIMENT    STATION 


By  similar  computations,  the  length  of  wire  necessary  to  produce 
this  amount  of  heat  in  non-glowing  heating  elements  can  be  deter- 
mined. (For  non-glowing  computations  the  temperature  assumed 
should  be  approximately  572°  F  and  should  not  exceed  800°  F.) 
Table  4  lists  results  of  computations  on  both  non-glowing  and  glowing 
heat  designs  and  may  be  used  in  the  design  of  brooder  heating 
elements  without  going  through  the  above  computations. 


TABLE  4 

Eesistance  Wire  Sizes  and  Lengths  to  Produce  ' '  Black  Heat  ' '  and  Glowing 
Surface  Temperatures  When  Consuming  Known  Wattages  at  110  Volts. 
For  "Nichrome"  Eesistance  Wire  of   660   OHMS   Specific   Eesistance, 
Part  "A" — Wire  Surface  Temperature:  About  572°  F,  Non-Glowing 


Required  wattage .... 

100 

200 

250 

300 

350 

400 

450 

500 

550 

600 

650 

Amperes  at  110  volts 

.909 

1.818 

2.27 

2.727 

3.180 

3.636 

4.09 

4.545 

5.00 

5.454 

5.91 

Resistance  in  ohms.. 

121.01 

60.51 

48.40 

40.33 

34.60 

30.25 

26.85 

24.19 

22.00 

20.17 

18.62 

Size  of  wire,  B  &  S 

gage  from  Current- 

temperature   chart 

31 

27 

25 

24 

23 

22 

22 

21 

21 

20 

20 

Resistance  of  wire  at 

68°  F,  ohms 

8.333 

3.274 

2.060 

1.634 

1.292 

1.031 

1.031 

.813 

.813 

.645 

.645 

Resistance  of  wire  at 

572°  F  ohms 

8.870 

3.485 

2.195 

1.739 

1.375 

1.099 

1.099 

.865 

.865 

.687 

.687 

Element   length    in 

feet,  at  572°  F 

13.64 

17.36 

22.10 

23.19 

25.14 

27.55 

24.50 

27.96 

25.45 

29.35 

27.10 

Part  "B" — Wire  Surface  Temperature  about  1472°  F ;  "Radiant  Eeat," 

Glowing 


Required  wattage.. 

100 

200 

250 

300 

350 

400 

'450 

500 

550 

600 

650 

Size  of  wire,  B  &  S 

gage,  Current-tem- 

perature chart 

35 

31 

30 

29 

28 

27 

26 

26 

25 

25 

24 

Resistance    of    wire 

at  68°  F,  ohms 

21.019 

8.333 

6.600 

5.168 

4.159 

3.274 

2.611 

2.611 

2.060 

2.060 

1.634 

Resistance    of    wire 

at  1472°  F,  ohms .... 

23.373 

9.263 

7.34 

5.747 

4.62 

3.641 

2.903 

2.903 

2.291 

2.291 

1.819 

Element    length    in 

feet .  . 

5.17 

6.54 

6.59 

7.02 

7.49 

8.31 

9.25 

8.34 

9.59 

8.80 

10.24 

Note. — Non-glowing  wire  smaller  than  No  25  gage  is  too  fine  for  successful  operation  in  brooders. 
"Radiant  heat"  wire,  smaller  than  No.  29,  is  also  impractical  for  brooder  use.  Therefore,  wattages 
under  250  are  impractical,  unless  long  wire  is  used  or  the  wire  is  of  extremely  high  resistance. 


VOLTAGE    DROP 


When  an  electric  current  flows  through  a  conductor,  a  drop  in 
voltage  occurs  along  the  wire  in  the  direction  of  flow.  This  drop  in 
voltage  is  analogous  to  the  drop  in  pressure  which  occurs  along  a  pipe 
carrying  water  from  a  tank  or  pump.     Should  this  stream  of  water 


BUL.  441]  THE   ELECTRIC    BROODER  35 

be  shut  off,  the  pressure  in  the  pipe  immediately  rises  to  a  value  equal 
to  the  static  head  of  the  system.  In  a  similar  manner,  when  an 
electric  current  is  interrupted  the  pressure  or  voltage  across  the  live 
terminals  of  the  switch  immediately  rises  to  a  value  equal  to  the 
voltage  of  the  system. 

This  drop  in  voltage  when  a  current  flows  should  be  kept  as  low  as 
is  economically  possible,  since  it  indicates  that  heat  is  being  developed 
in  the  conductor  and  dissipated  into  the  atmosphere  where  it  can  do 
no  good.  Usually  a  voltage  drop  in  excess  of  5  per  cent  will  prove 
uneconomical. 

To  illustrate  the  extent  of  this  loss  when  long  leads  are  used,  it 
was  found  during  one  test  that  81.8  amperes  were  being  carried  from 
the  meter  to  the  poultry  house,  a  distance  of  400  feet,  by  No.  2 
weather  proof  copper  wire.  The  total  length  of  wire  necessary  then 
to  carry  the  current  to  the  brooders  and  back  again  will  be  2  times 
400  feet  or  800  feet.  The  resistance  of  No.  2  copper  wire  at  68°  F  is 
(from  table  1)  .1563  ohms  per  1000  feet.  The  resistance  of  800  feet 
is  .8  times  .1563  or  .1250  ohms.  The  power  lost  as  heat  in  the  con- 
ductor was  the  current  in  amperes  squared  times  the  resistance,  or 
81.8  X  81.8  X  .1250  or  836.4  watts.  If  this  current  flows  24  hours  a 
day  for  the  three  months  of  the  brooding  season,  the  loss  will  be  836.4 
(watts  per  hour)  times  24  (hours  per  day)  times  90  (days)  or  1,806.6 
kilowatt-hours.  At  2  cents  per  kilowatt-hour  this  represents  a  loss  of 
2  X  1806.6,  or  $36.13.  The  drop  in  voltage  from  meter  to  load  was 
836.4  watts  divided  by  81.8  amperes  or  10.2  volts. 

Assume  now  a  voltage  drop  not  greater  than  5  per  cent  in  the 
power  leads  from  this  meter  to  the  load,  which  on  the  110-volt  circuit 
will  give  110  (volts)  times  5  (per  cent)  or  5.5  volts  drop.  The  power 
now  converted  into  heat  in  these  leads  will  be  5.5  (volts)  times  81.8 
(amperes)  or  449.9  watts.  During  the  three  months  of  the  brooding 
season,  this  will  amount  to  971.8  kilowatt-hours  or,  at  2  cents  per 
kw-hr.,  $19.44.  The  conductor  required  for  a  5  per  cent  drop  in 
800  feet  when  81.8  amperes  are  flowing  will  have  a  resistance  of 

449.9  (watts) 


81.8  X  81.8 


(amperes)  or  .0672  ohms.    A  thousand  feet  of  this  con- 


ductor will  have  a  resistance  of  - — ^  or  .0840  ohms.     From  table  1 

.0 

the  wire  having  a  resistance  nearest  to  this  figure  is  No.  00,  which  has 
a  resistance  of  .0779  ohms  per  1000  feet.  Therefore,  if  a  voltage  drop 
not  to  exceed  5  per  cent  is  to  be  allowed,  the  conductor  used  should 
be  No.  00  weatherproof  copper  wire. 


36 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 


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BUL.  441]  THE   ELECTRIC    BROODER  37 

It  should  be  remembered  that  this  loss  in  power  due  to  a  voltage 
drop  occurs  only  when  a  current  is  flowing  through  the  wire.  There 
is  practically  no  loss  when  the  line  is  not  being  used. 

The  larger  wire  will  cost  considerably  more  to  install,  since  the 
same  length  (800  feet)  weighs  almost  twice  as  much.  Will  it  be 
economically  sound  to  make  this  additional  investment  in  the  power 
leads  ? 

The  weight  of  No.  2  weatherproof  copper  wire  required  for  the 
800  feet,  according  to  table  1  is  260  X  -8  or  208  pounds,  while  the 
weight  of  No.  00  is  502  X  .8  or  401.6  pounds.  The  extra  copper  then 
which  must  be  purchased  if  No.  00  is  used  is  401.6  minus  208  or 
193.6  pounds.  The  cost  per  pound  of  this  wire  will  average  25  cents. 
The  additional  investment  in  the  line,  due  to  heavier  wire,  will  be 
193.6  (pounds)  times  25  (cents  per  pounds)  or  $48.40. 

Applying  the  reasoning  set  forth  under  Economics  of  New  Devices, 
page  6,  the  following  figures  result :  If  correctly 

As  installed    installed 

Additional  copper  costs  193.6  lbs.  at  25  cents  per  pound $48.40 

Additional  interest  at  6  per  cent  of  one-half  value $1.45 

Yearly  additional  depreciation  (10-year  life)   $4.84 

Repairs,  taxes,  insurance  and  overhead,  same  for  both 

Loss  due  to  line  resistance  $36.13  $19.44 

$36.13  $25.73 

Savings  affected  by  use  of  larger  copper  $10.40 

If  the  transformer  bank  had  been  centrally  located  with  respect  to 
the  load,  as  is  often  possible,  a  considerable  saving  in  the  cost  of  the 
wire  would  have  resulted.  For  best  results,  the  meter  should  not  be 
more  than  200  feet  from  where  the  power  is  being  absorbed. 


SAFETY  PRECAUTIONS 

In  working  with  any  electrical  circuit,  it  is  well  to  remember  the 
following : 

1.  Never  attempt  to  work  with  a  "hot"  or  live  circuit.  Open  the 
circuit  switch  or  remove  the  circuit  fuses  first.  While  110  volts  will 
seldom  injure  one,  there  are  conditions  under  which  it  may  be 
injurious. 

2.  Consider  all  electric  wires  "hot"  unless  you  have  opened  the 
circuit  yourself  or  know  it  to  be  open. 

3.  If  a  shock  is  received  from  the  ordinary  electrical  appliances, 
determine  the  cause  at  once.  It  generally  indicates  poor  electrical 
insulation. 


38  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION 

4.  Never  work  with  a  power  circuit  when  standing  on  wet  ground 
or  wet  floors,  or  when  in  water. 

5.  Never  allow  the  body  to  become  a  part  of  a  circuit.  The  body 
can  form  a  circuit  either  to  "ground"  or  to  the  opposite  power  "leg." 

6.  Always  remember  that  both  legs  of  an  alternating  current 
circuit  as  usually  operated  are  "live." 

7.  Fuse  the  circuits  on  both  legs  and  fuse  for  about  125  per  cent 
of  full  load.  These  fuses  will  protect  your  electrical  apparatus  and 
the  circuit. 

SUMMARY  AND  CONCLUSIONS 

The  electric  brooder  is  heated  with  electric  heating  elements  and 
makes  use  of  radiation,  convection  or  conduction  for  transfering  heat 
from  the  elements  to  the  space  occupied  by  the  chick. 

When  radiation  is  depended  upon  as  the  method  of  heat  transfer 
and  the  elements  are  operated  at  glowing  temperature,  the  hover  is 
generally  three  to  four  feet  high,  no  curtains  are  used  and  little  or 
no  trouble  will  be  experienced  from  "sweating."  The  heating  cost 
at  2  cents  per  kilowatt-hour  will  average  about  2.5  to  3  cents  per 
chick  each  1000  hours. 

For  mild  climates  2  watts  should  be  allowed  per  chick  and  where 
freezing  temperatures  are  experienced  2.5  to  3  watts  should  be 
available. 

Because  of  the  high  temperature  of  the  elements  there  is  a  slightly 
greater  fire  hazard  than  is  found  in  the  ' '  black  heat ' '  type. 

In  brooders  using  radiation  but  equipped  with  elements  that  do  not 
glow  the  hover  is  low,  usually  has  curtains,  and  has  some  special 
provision  for  taking  care  of  air  replacement.  Operation  costs  are 
somewhat  lower  than  with  the  "glowing"  type.  The  heaters  should 
have  a  capacity  of  from  1.5  to  2  watts  per  chick. 

The  brooders  depending  upon  convection  usually  heat  some  or  all 
of  the  incoming  air,  may  or  may  not  use  curtains,  may  use  either  the 
glowing  or  non-glowing  elements,  are  comparatively  free  from  sweat- 
ing troubles,  and  cost  from  %  of  a  cent  to  1  cent  per  chick  for  each 
1000  hours  to  heat. 

Due  to  the  tendency  of  the  moisture  to  condense  on  the  chick's 
feathers  under  certain  conditions  the  removal  of  the  tainted  air  is  of 
prime  importance  in  all  types.  Some  brooders  have  provision  for 
positive  ventilation,  others  have  not.  The  open  or  curtainless  type  of 
hover  requires  more  heat  than  the  closed  or  curtain  type  but  it  has 
better  ventilation. 


Bul.441] 


THE   ELECTRIC    BROODER 


39 


Seven  square  inches  is  the  brooder  floor  area  recommended  per 
chick.  If  a  smaller  space  is  used  less  heat  will  be  required  but  ven- 
tilation troubles  will  probably  be  greater.  The  chief  difference  between 
brooders  lies  in  the  comparative  cost  and  dependability  of  operation. 
Those  that  conserve  the  heat  by  means  of  curtains,  crowding  or 
restricted  ventilators  will  cost  less  but  will  be  less  satisfactory  than 
those  less  careful  of  the  heat  but  more  careful  of  ventilation. 

In  general,  brooders  using  non-glowing  coils  also  use  curtains 
while  those  using  glowing  elements  do  not. 

Table  6  follows,  which  is  a  condensed  summary  of  the  results  of 
tests  conducted  by  the  California  Committee  on  the  Relation  of 
Electricity  to  Agriculture  during  this  investigation. 


TABLE  C 

Condensed  Summary  Electric  Poultry  Brooder  Tests,  All  Types  1925,  19: 
Conducted  by  the  California  Committee  on  the  Eelation  of 
Electricty  to  Agriculture 


Non-glowing 
Brooder  tests. 

"Radiant" 

or  glowing  type 

brooder  tests 

8 

33 

21940 

18121 

3819 

8596.9 

665 

17.4 

.474 
1.298 
974 
4.88 
.948  cents 

6 

Total  number  tests  run 

16 
10994 

9532 

1462 

Total  kilowatt-hours  consumed 

14810.0 
687 

Average  mortality,  per  cent 

13.3 
1.553 

Average  connected  load  per  chick,  watts 

Average  brooding  season,  hours 

Average  brooder  area,  square  inches 

Average  cost  per  cnick,  (2  cents  per  kw.-hr.  base) 

1.908 
1200 
7.83 
3.110  cents 

ACKNOWLEDGMENTS 

The  writers  are  indebted  to  the  following  poultrymen  who  have 
generously  cooperated  and  permitted  the  study  and  testing  of  their 
electric  brooders :  L.  Bufford,  Santa  Rosa ;  J.  J.  Burke,  Santa  Rosa ; 
H.  Cook,  Santa  Rosa;  F.  Ehrlick,  Santa  Rosa;  J.  O.  Freisinn,  Santa 
Rosa;  P.  Randolph,  Santa  Rosa;  M.  Schulz,  Santa  Rosa;  E.  O.  Hussey, 
Petaluma;  D.  B.  Walls,  Petaluma;  Grace  N.  Johnson,  Healdsburg; 
P.  Mothorn,  Healdsburg;  and  E.  S.  Williams,  Sebastopol.  The  follow- 
ing have  also  assisted  in  numerous  ways :  M.  W.  Buster,  Specialist  in 
Agricultural  Extension ;  J.  W.  Felt,  Great  Western  Power  Company, 
Santa  Rosa;  W.  W.  Shuhaw,  Pacific  Gas  &  Electric  Company,  Santa 
Rosa,  and  the  Poultry  Husbandry  Division  of  the  University  of 
California. 


12n?-ll,'27 


